In vehicles, evaporative fuel which leaks into the ambient air from a fuel tank, etc., is described as one of the causes of air pollution because of the large content of hydrocarbons (HC). The evaporative fuel also contributes to fuel loss. Accordingly, various techniques are known as a prevention thereagainst, and an evaporative fuel controller (an evaporation system) is representative of one such technique. In this controller, evaporated fuel from the fuel tank is absorbed by a canister which contains an absorbent such as activated carbon. The absorbed fuel is released (purged) from the canister during operation of an engine, and is then supplied to the engine.
The above-described controller is disclosed, e.g., in published Japanese Patent Application Laid-Open No. 7-279788. A controller disclosed in this publication includes the following: a shutter disposed on the top of a filler tube, the shutter being opened by the insertion of a fuel-feeding nozzle therein; a vent tube for communicating between an upper space in a fuel tank body and a canister; a fuel supercharge-preventing valve positioned at the end of the vent tube extending over inside the fuel tank body; a vent cut valve provided substantially midway along a line of the vent tube for closing the line of the vent tube in response to opening and closing movement of the shutter; and, a clearance provided on a side wall of the filler tube for communicating a space in the vent tube between the fuel supercharge-preventing valve and the vent cut valve with an upper space in the filler tube. The evaporated fuel controller thereby prevents stoic of the fuel supercharge-preventing valve without increases in dimensions and weight of the same valve, and further prevents a rise in liquid level in the filler tube when temperature inside the fuel tank body rises.
Referring to FIG. 7, a conventional evaporative fuel controller is illustrated, in which reference numeral 2 denotes an internal combustion engine disposed in a vehicle (not shown); 4 an intake manifold; 6 an intake passage; 8 a surge tank; 10 a throttle valve; 12 a fuel injection valve; 14 an air cleaner; and, 16 a fuel tank.
The fuel tank 16 has a fuel-feeding pipe (filler hose) 20 incorporated therein. A fuel-feeding cap 18 is positioned on the pipe 20. The pipe 20 has a fuel-feeding passage (filler passage) 22 formed therethrough.
The fuel tank 16 has the following provided therein: a fuel pump (not shown); a tank pressure sensor 24; a refueling vapor control valve 26 and a float valve 28, the control valve 26 including a float valve body (not shown) which is moved upward and downward, depending upon fuel quantity; and, a level gauge 30 for detecting the fuel quantity. The refueling vapor control valve 26 is positioned at a substantially central portion of the tank 16. The float valve 28, which is smaller in dimension than the control valve 26, is located at a position spaced apart from a central portion of the tank 16. The fuel pump is communicated to one end of a fuel supply passage (not shown). The other end of the fuel supply passage is communicated to the fuel injection valve 12. The fuel injection valve 12 has a fuel pressure regulator 32 arranged in series therewith. The fuel pressure regulator 32 is communicated to one end of a fuel return passage (not shown). The other end of the fuel return passage is positioned and opened in the fuel tank 16.
A positive pressure type of evaporative fuel controller (evaporation system) 34 is provided between the fuel tank 16 and an intake system of the engine 2. In the evaporative fuel controller 34, one end of each of first to third evaporation passages 36, 38, and 40 communicates with the inside of the fuel tank 16, while one end of a purge passage 42 communicates with the surge tank 8 which constitutes the intake passage 6. Further, a canister 44 is located between the other end of each of the evaporation passages 36, 38, 40 and the other end of the purge passage 42.
More specifically, one end of the first evaporation passage 36 is provided in communication with the refueling vapor control valve 26 in the fuel tank 16. One end of the second evaporation passage 38 communicates with the third evaporation passage 40 at a location substantially midway therealong. And, one end of the third evaporation passage 40 is positioned inside a float guide body 46 at a location spaced apart from the top of the tank 16 by a predetermined distance so as to be opened and closed by the float valve 28. In the fuel tank 16, the float valve 28 is guided and moved upward/downward inside the float guide body 46. In the fuel tank 16, there exists a gap between the ends of the first and third evaporation passages 36 and 40.
The other end of the first evaporation passage 36 is communicated to the top of the canister 44. The other end of the second evaporation passage 38 communicates with the third evaporation passage 40 at a location substantially midway therealong. The other end of the third evaporation passage 40 is communicated with the top of the canister 44.
The refueling vapor control valve 26 is provided with a float valve body 26G (FIG. 8); and, first and second chambers in which the first chamber 26B is a pressure-working chamber while the second chamber 26C is a passage communication chamber. The first and second chambers are defined and partitioned by a partition body 26D, or a diaphragm, within a housing 26E. In addition, the first chamber has a spring 26F provided therein for pressing the diaphragm. Further, a valve seat body is provided for causing the first evaporation passage 36 to be opened and closed by a central portion of the diaphragm being brought into contact with and movement away from the valve seat body in the second chamber. The first chamber and the fuel-feeding passage 22 are communicated to one another through a tank-side communication passage 48.
A solenoid valve 50 is disposed along the second evaporation passage 38. The valve 50 is formed by a conventional two-way electromagnetic valve.
The third evaporation passage 40 is provided with an internal tank pressure control valve, or rather a pressure control valve 52. The pressure control valve 52 provides an opening action so as to open the third evaporation passage 40 when the internal pressure of the fuel tank 16 exceeds a predetermined pressure during stopping of the engine 2. The pressure control valve 52 is formed by a check valve. The check valve includes a partition body and a check body within a housing (not shown). The check body is provided on the partition body.
The other end of the second evaporation passage 38 communicates with the third evaporation passage 40 at a location toward the canister 44, i.e., between the canister 44 and the pressure control valve 52, whereby the other end of the second passage 38 bypasses the pressure control valve 52. In addition, the aforesaid predetermined pressure is a pressure value at which the pressure control valve 52 is caused to provide a closing action, even when the fuel tank 16 is being supplied with fuel.
A purge valve (solenoid valve) 54 is disposed along the purge passage 42 for controlling an amount of evaporated fuel in accordance with an operating state of the engine 2. The evaporated fuel is to be fed into the intake passage 6.
The other end of the first to third evaporation passages 36, 38, 40 and the other end of the purge passage 42 are arranged in a side-by-side array and opened within the top of the canister 44. The canister 44 is communicated to one end of an atmosphere communication passage 56. The atmosphere communication passage 56 has the following positioned toward the other end thereof: an air-cut valve (solenoid valve) 58 for opening and closing the atmosphere communication passage 56; and, an air cleaner 60.
The canister 44 absorbs and retains evaporated fuel which is generated in the fuel tank 16 and is then introduced into the evaporation passages 36, 38, and 40. The absorbingly retained fuel is liberated from the canister 44 by the ambient air introduced through the atmosphere communication passage 56 during operation of the engine 2. The liberated fuel is then supplied to the intake passage 6 through the purge passage 42.
The fuel injection valve 12, the solenoid valve 50, the purge valve 54, and the air-cut valve 58 all communicate with the control means 62.
As illustrated in FIG. 8, the refueling vapor control valve 26 and the solenoid valve 50 are closed before fuel supply to the fuel tank 16. In addition, the pressure control valve 52 retains the internal tank pressure of the fuel tank 16. When the internal tank pressure is greater than a predetermined pressure, then the pressure control valve 52 is operated to open the third evaporation passage 40. Then, the evaporated fuel generated in the tank 16 is absorbed by the canister 44 through the third evaporation passage 40.
As illustrated in FIG. 9, a negative pressure is established in the first chamber 26B of the refueling vapor control valve 26 during the feeding of fuel into the tank 16, and then the refueling vapor control valve 26 is opened. Thus, the evaporated fuel in the fuel tank 16 is absorbed by the canister 44 through the first evaporation passage 36.
Then, the evaporated fuel absorbed by the canister 44 is purged into the intake passage 6 through the purge passage 42 in accordance with an operating state of the engine 2.
Referring now to FIG. 10, the refueling vapor control valve 26 and the solenoid valve 50 are shown closed after fuel supply to the tank 16. In addition, the pressure control valve 52 retains the internal pressure of the tank 16.
Referring to FIG. 11, the refueling vapor control valve 26 and the pressure control valve 52 are closed during operation of the engine 2. However, the solenoid valve 50 is opened, and the evaporated fuel in the fuel tank 16 passes through the second evaporation passage 38 and a portion of the third evaporation passage 40 and is absorbed by the canister 44.
As illustrated in FIG. 12, when the tank 16 is filled up with fuel immediately after the supply of fuel thereto, then pressure P1 in the first chamber of the refueling vapor control valve 26 and pressure P2 in the fuel tank 16 are related as:
P2&gt;P1 PA1 P2'&gt;P1'
Assuming that a difference between the fuel level in the fuel-feeding pipe 20 and the fuel level in the fuel tank 16 is h1 (mmHg), then difference h1 (mmHg) added to pressure P1 is substantially equal to pressure P2.
Turning now to FIG. 13, the refueling vapor control valve 26 is illustrated opened during running of a vehicle after the fuel tank 16 is filled up with fuel. In addition, the canister (not shown) and the inside of the fuel tank 16 are communicated with one another through the first evaporation passage 36. Then, a relationship between pressure P1' in the first chamber of the refueling vapor control valve 26 and pressure P2' in the fuel tank 16 are described as:
Assuming that a difference between one fuel level in the fuel-feeding pipe 20 and another in the fuel tank 16 is h2' (mmHg), then difference h2' (mmHg) added to pressure P1' is substantially equal to pressure P2'.
In conclusion, there occurs a pressure differential between the pressure in the first chamber 26B of the refueling vapor control valve and the pressure in the fuel tank 16. When the pressure differential overcomes the urging force of the refueling vapor control valve, then fuel and/or evaporated fuel in the fuel tank is caused to flow into the canister 44 during deactivation and activation of the engine. This causes inconveniences in that the fuel/evaporated fuel deteriorates the canister, thereby failing to insure canister performance, with a consequential increase in evaporative emissions.